Took me a bit to figure out how the carrier plate ever gets unlocked, that is neat
Just don't apply power while actuating the PTO cylinder!
It's hard to imagine you're using the CIM encoder to line up the locking notches with the cylinder. Can the rounded end of the locking pin ride up the outer contour to get into the notch? Why not make the locking notch the only groove, so the locking pin rides the OD until it engages? Like the locking plate on 118's arm in 2014:
http://s22.postimg.org/3sk056lxt/Scr...3_19_25_33.png
Also, for the locking pins, I wonder if you could use something like mcmaster 84835A22 to reduce friction if you want to actuate the PTO cylinder and slide it in into place. You'd have to turn the gearbox slowly to avoid wrecking the lock after PTO engage and before drive disengage.